Soil grouting process

ABSTRACT

In a process for stabilizing soil by impregnation with an alkaline aqueous gel-forming composition containing (a) a polyphenolic material such as a vegetable tannin extract and (b) a formaldehyde compound such as paraformaldehyde, a surprising improvement in control of gelling rate is achieved by including in said composition a precalculated amount of (c) gelling agent dispersible in said composition and containing a complexing element selected from silicon, vanadium, molybdenum, manganese, titanium, copper, zinc and zirconium.

United States Patent Whitworth et al.

[ Aug. 29, 1972 [54] SOIL GROUTING PROCESS [72] inventors: Anthony JamelWhltworth, 65 Commonwealth Ave., Scarborough [58] Field ofSearell...61I36 R; 166/295; 260/172 R, 260/293. 38. DIG. 14, 17.2 S

[56] References Cited UNITED STATES PATENTS 3,391,542 7/1968 Herrick etal ..61/36 R 2,652,373 9/1953 Avedikian ..260/17.2 3,025 ,250 3/ 1962Herrick et a1 "260/112 3,530,081 9/1970 Herrick et al ..260/38 X FOREIGNPATENTS OR APPLICATIONS 1,122,308 8/1968 Great Britain ..61/36 R OTHERPUBLICATIONS Lewis et al., Colloidal Properties of Clay SuspensionsTransactions, AIME, Vol. 114, 1935, pages 38- 52.

Rogers, Composition and Properties of Oil Well Drilling Flui ThirdEdition, Gulf Publishing Co., Houston, Tex. 1963, pp. 334- 339.

Chem. Abstracts, 54:9443e (The Effect of Soluble Salts on the Gelationof Tannin-Fonnaldehyde) fi-imary Examiner-Stephen J. NovosadAttorney-Edward L. Mandell, George P. Maskas and George A. Kap

[ ABSTRACT In a process for stabilizing soil by impregnation with analkaline aqueous gel-forming composition containing (a) a polyphenolicmaterial such as a vegetable tannin extract and (b) a formaldehydecompound such as paraformaldehyde, a surprising improvement in controlof gelling rate is achieved by including in said composition aprecalculated amount of (c) gelling agent dispersible in saidcomposition and containing a complexing element selected from silicon,vanadium, molybdenum, manganese, titanium, copper, zinc and zirconiuml2C1aims,NoDrawings SOIL GROUTING PROCESS BACKGROUND OF THE INVENTIONThis invention relates to a grouting process and grouting compositionsfor stabilizing soil. Grouting is the term used to denote the process ofstabilizing sand, soil or similar substrates in order to increase thestrength and load bearing characteristics of the area and to seal offwater or liquid flows in the grouted area. Such consolidation of loosesoils and subsoils by impregnating, mixing with or injecting into thesoil, substances having a binding action of great importance in manycivil engineering, mining and drilling operations. There is, therefore,a demand for compositions which can be injected into porous ground so asto form a substantially compact and impervious mass.

The term soil" is used herein to designate any geological matter havingsufficient porosity to permit impregnation by the method of the presentinvention. The present invention has particular utility in the treatmentof subterranean strata of finely porous structure, such as sandstone, byinjecting the grouting composition into the strata under pressure, e.g.any pressure above atmospheric, depending on the porosity of the soil.

in British Pat. spec. No. 1,122,308, a method is described and claimedfor the stabilization of soil which comprises treating the soil with anaqueous liquid composition comprising (a) a vegetable tannin extract,(b) formaldehyde and/or paraformaldehyde or a watersolublephenol-formaldehyde resole and (c) an alkalimetal hydroxide and allowingthe treated soil to harden.

While this method is effective for the purposes intended, thecompositions used therein require such long periods of time to solidifyor gel that in certain locations where the soil is very porous, largequantities of grouting solution are lost by seeping too far into theporous structure before the penetrated mass is made impervious. Becauseit is thus difficult to control, modify or accelerate the gelling time,cumbersome adaptations in procedure must be made to decrease flow ratesuch as adding varying amounts of polymeric thickening agents toincrease viscosity or such as making fine adjustments in the injectionpressure. Furthermore it is difficult to get good results with themethod of the above cited patent when the ground to be grouted is cold,the cost of using hot grouting solutions being prohibitive and difficultto control.

More specifically, with tannin formaldehyde grouting solutions of theabove cited patent, even with addition of 4 percent of a water-solublesalt of calcium, magnesium or aluminum as suggested therein, gelationtimes of approximately 2 hours or longer are encountered at 25 C. Attemperatures less than 25C. the gel time increases as the temperature islowered until at around 7C. it is extremely difficult to obtain any gelat all and the composition is ineffective as a grouting material.Similar deficiencies are experienced with systems in which all or partof the tannin is replaced by catechins or by polyphenolic materialsobtained by extraction of coniferous tree barks.

As to other types of grouting methods and compositions which have beenproposed, on one hand there are the traditional procedures based oncement and on the other hand there are several chemical grouts" whichhave aimed to overcome the deficiencies of cement but which themselveshave various deficiencies. The severe limitations of cement result fromthe fact that the grout itself is particulate and is consequently unableto penetrate fine substrates. Furthermore, cement systems haverelatively long and uncontrollable curing rates which make cement groutsimpractical for cutting off fast flowing water.

Among the chemical systems, one based on the polymerization ofacrylamide and NN-methylene bisacrylamide has the disadvantages of highcost, high toxicity, low structural strength and considerablecontraction in the absence of water. Another based on magnesiumacrylate, methylene bisacrylamide and acrylonitrile has similardisadvantages. A chrome-lignin process has the disadvantages thathexavalent chromium is toxic and hazardous to handle; also theviscosities of initial grout solutions before gelling are excessivelyhigh.

Grouts have also been disclosed with sodium silicate as principalcomponent in admixture with reagents such as lime slurry, sodiumbicarbonate, copper sulfate and aluminum salts. In such prior artcompositions the silicate content is between about 30 to 50 percent, thestrengths of gel obtainable are low and there is no perceptible increasein the strength of the grouted soil.

SUMMARY OF THE INVENTION A method has now been found whereby an aqueousalkaline polyphenolic-formaldehyde grouting composition can be made toget in a precalculated time by including in said composition a carefullycontrolled proportion of a compound dispersible therein and derived froman element selected from silicon, vanadium, molybdenum, manganese,titanium, copper, zinc and zirconium.

Since these elements all possess the tendency to form complexes inalkaline aqueous solution with water and with hydroxyl ions, they aredesignated herein as complexing elements.

Most of these complexing elements form true solutions in the aqueousgrouting compositions, being present largely as hydroxylated or hydratedanions such as silicate, vanadate, molybdate, zincate, and the like.However in some instances, at least part of the element present iscontained in the form of a colloid dispersion or hydrosol such as zinchydroxide hydrosol. The terms dispersibleand dispersion as used hereinare intended to include soluble" and solution" respectively.

Unexpectedly, compositions of the present invention are capable offorming gels quite rapidly at temperatures close to freezing as forexample at 5C.

Briefly stated, the method of this invention includes the steps of (A)treating the soil with an aqueous alkaline gel-forming liquid comprising(a) a polyphenolic material selected from vegetable tannin extracts,catechins and tree bark extracts, said polyphenolic material beingsoluble in alkaline solution able to gel rapidly and able to combinewith formaldehyde (b) a formaldehyde compound selected fromformaldehyde, paraformaldehyde and a water-soluble phenolformaldehyderesole and (c) a gelling agent dispersible in said composition andcontaining a complexing element selected from silicon, vanadium,molybdenum, manganese, titanium, copper, zinc and zirconium; and (B)allowing the treated soil to form a substantially compact mass. Theinvention also includes the grouting compositions used in carrying outsaid method.

By careful control of the relative proportion of the gelling agent, thetime required to form the gel or solid phase of the grouted structurecan be precisely controlled to take place over a period selected fromthe range from about one second to several hours after injection, asneeded for suitable placement of the grout.

it has been surprisingly found that gelling agents of this invention notonly accelerate the gelling action but also result in a groutedstructure which has a stronger resistance to compressive forces than isdeveloped by the same compositions without the gelling agent.

The gelling agents of this invention are effective in relatively smallamounts, some of the advantages of the invention being observable withas little as 0.01 percent of complexing element based on weight of thepolyphenolic material component. The efficiency of sodium silicate insuch small amounts is surprising in comparison with the aforementionedgrouts of prior art requiring solutions containing sodium silicate inconcentrations as high as 30 to 50 percent by weight.

DETAILED DESCRIPTION The grouting process and composition of thisinvention have the advantages that the raw materials used are cheap,readily available, dispersible in aqueous al kaline solution at lowtemperatures, and easy to apply on site.

The grouting process of this invention is capable of adjustment, byvariation of the components, to have a large controllable range of geltimes over a wide range of temperature and climatic conditions toachieve accurate placement of grout solution into the substrate.

Since the dispersions of this invention have low initial viscosity,comparable to water, deep penetration into finely pored substrates isfacilitated. But when less deep penetration is desired, as when the soilis easily penetrated because of larger pore size, the relativeproportion of gelling agent in the composition can be increased toattain quick gelation.

The compositions of this invention have relatively low toxicity and areeasily handled by inexperienced operating personnel.

Treatment of soil with grouting compositions of this invention canproduce grouted soil which is stable and possesses the required loadbearing properties. The grouted substrate is also resistant todeterioration by atmosphere and by water.

Polyphenolic materials suitable for use in the present invention includevegetable tannins such as those extracted from mimosa, quebracho,mangrove and wattle; catechin and catechu such as extracted from acaciacatechu and acacia suma, mahogany wood and the like; and the alkalineextracts of certain coniferous tree barks including the barks of Westernhemlock, Douglas fir, white fir, Sitlta spruce and Southern yellow pineparticularly such as prepared by the methods of US. Pat. Nos. 2,782,24l;2,819,295 and 2,823,223.

The preferred polyphenolic material is the readily available vegetabletannin extract known as mimosa extract, an extract from acaciamollissima, and the invention is illustrated by particular reference tothis material. Other vegetable tannin extracts include those obtainedfrom eucalyptus crebra, callitris calcarata and callitris glauca.

While all the aforementioned polyphenolic materials are commerciallyavailable, their exact chemical constitution is not known. Utility of aparticular product in carrying out this invention is based on possessionof three properties, namely solubility in alkaline solutions, ability togel rapidly in the compositions of this invention and ability to combinewith formaldehyde.

The ability to combine with formaldehyde is conveniently measured as thegrams of formaldehyde which react in four hours with grams of the drycommercial polyphenolic product dissolved in aqueous solution of pH 9.5.Such an alkaline solution containing accurately known amounts ofpolyphenolic product and of formaldehyde is allowed to stand for fourhours, the remaining formaldehyde is accurately determined and thereacted formaldehyde is calculated by dif ference. A suitable method fordetermining formaldehyde is given by Lemme, Chem.Ztg. 27, 896 i903 To beuseful in the present invention the formaldehyde combining capacity ofthe polyphenolic material measured as the ratio of reacted formaldehydeto polyphenolic material on dry basis should be at least about 5.0.

The concentration of said polyphenolic material in the aqueous groutingdispersion can be in the range of about 2 to 45 percent. However, higherconcentrations in this range correspond to dispersions of high viscosityand are applicable only when the soil has sufficiently highpermeability. On the other hand, since the strength obtainable in thegrouted soil decreases with decreased concentration of polyphenolicmaterial, the lowest concentrations in the stated range are suitableonly when it is sufficient to render the soil merely impervious. Toobtain the benefits of high strength of grouted soil as well as theopportunity to control gel time, it is preferred to have thepolyphenolic material at a concentration level of between about 4-27percent, more particularly 7-23 percent of the weight of the aqueouscomposition.

The preferred amount of formaldehyde to be used in the compositions ofthis invention is between about 15 and 25 parts by weight to every I00parts of polyphenolic material on a dry basis. There is no precise upperlimit, but for reasons of economy and fume control it is not normallydesirable to exceed 30 parts of formaldehyde to every 100 parts ofpolyphenolic solids. As to the lower limit, as little as 5 partsformaldehyde for every 100 of polyphenolic has been found effective.When sodium silicate is used as the gelling agent, it has been foundthat the formal dehyde can be omitted entirely.

Paraforrnaldehyde is the preferred source of form aldehyde because ofits low tendency to fume and because it can be formulated with thetannin extract as a powder before dissolving to make the groutingsolution.

An alternative source of formaldehyde is a watersoluble phenolformaldehyde resole such as prepared for example by reacting 1 molarproportion of phenol with 1.5 to 3 molar proportions of formaldehyde inthe presence of an alkali metal hydroxide catalyst. Between about 2 and3 parts by weight of such phenolic resole solids can be used in place ofone part of formaldehyde.

The gelling agents of this invention can be selected from the aqueousalkali dispersible compounds of silicon vanadium, molybdenum, manganese,titanium, copper, zinc and zirconium.

These complexing elements are amphoteric, all having in some degree theattributes of both metallic and non metallic elements. Thus they aredispersible in the alkaline aqueous grouting composition of thisinvention largely as hydroxylated or hydrated anions. However, dependingon the degree to which the metallic or nonmetallic propertiespredominate, the solution may contain also cations or hydroxidehydrosol. Thus a zirconate solution contains a minor concentration ofzirconium cations in equilibrium with the zirconate ions, and a zincatesolution is known to contain some zinc hydroxide hydrosol.

The gelling agent can therefore be introduced into the aqueous groutingcomposition of this invention in a form in which the complexing elementis already anionic, as in the case of the silicates and molybdates ofthe alkali metals. Alternatively, the gelling agent can be added to thealkaline composition in a form in which the complexing element iscationic or non-ionized and which is chemically converted on hydrolysisby an alkaline medium into a predominantly anionic form. The latter isthe case, for example, when vanadium pentoxide is used as gelling agent;this substance is largely converted by hydrolytic action of the alkalinemedium to the anionic form of vanadate. Likewise, it is known that thealkali soluble salts of zinc and zirconium cations can be present inalkaline solution as zincate and zirconate respectively.

In the instances where the complexing elements of this invention have aplurality of valence states their compounds are effective as gellingagents in the different valence states. Thus both cuprous and cupriccompounds are gelling agents in the grouting composition of thisinvention.

In short, the gelling agent can exemplarily be an alkali-dispersiblesalt of silicate, vanadate, molybdate manganate, permanganate, titanate,cuprate, zincate or zirconate. lllustratively, such a salt can be apotassium, sodium, lithium or ammonium salt of any of these anions.Alternatively, the gelling agent can also be any chloride, sulfate,nitrate, hydroxide or oxide of any of the stated elements whichcompounds are dispersible in aqueous alkaline solutions. lllustratively,such compounds include zirconium tetrachloride, copper sulfate,manganous nitrate, zinc hydroxide and vanadium pentoxide.

in greater detail, examples of gelling agents which can be used inoperating the method of this invention include sodium metasilicate(Na,SiO;,), sodium metasilicate nonahydrate (Na,SiO '9H,O), commercialsodium silicate solutions having different ratios of Na,0 to SiO, suchas "egg-preserver solution" containing about 40 percent Na Si O-potassium silicate of variable composition (K 830, to K,Si 01), ammoniumfluosilicate, vanadium pentoxide, vanadyl chloride, vanadyl triehloride,ammonium metavanadate, molybdenum trioxide, ammonium molybdate, sodiummolybdate, potassium molybdate, manganous chloride, manganous nitrate,manganous sulfate, potassium manganate, potassium permanganate, ammoniumpermanganate, potassium titanate, sodium titanate, cuprous chloride,cupric chloride, cupric sulfate, zinc chloride,

zinc sulfate, zinc oxide, zinc hydroxide, zirconium nitrate, zirconylnitrate, and zirconium tetrachloride.

The preferred gelling agents, because of cheapness and facility ofsolution, are commercial grades of sodium silicate or vanadiumpentoxide.

As to the amounts of gelling agent which can be used in carrying outthis invention, extremely small quantities corresponding to as littleas0.0l percent of complexing element, based on the dry weight ofpolyphenolic material, have been found to be measurably effective on therate of gellation. The amount required to obtain a desired gel timedepends upon the dilution of the polyphenolic component and formaldehydegrouting components and the pH as well as the nature of the soil to begrouted and the identity of the gelling agent. Up to 10 percent ofcomplexing element, based on dry polyphenolic material could be usedunder certain combinations of these parameters, but in the interest ofeconomy, conditions which permit lower amounts are preferable. ingeneral, amounts corresponding to between about 0.1 and 6.5 percent ofcomplexing element based on polyphenolic solids are suitable.

in the typical practice of this invention, suitable polyphenolicmaterial is dispersed in sufficient water containing sufiicient alkalito form a dispersion of the desired concentration (in the range 2-45percent by weight of solution) and the pH is adjusted to between 8.5 andl 1.5 (preferably between 9.0 and l0.5) For the purpose of adjusting pH,sodium hydroxide, potassium hydroxide, sodium carbonate, potassiumcarbonate, or equivalent alkali can be used. The amount of alkali neededto attain such pH will depend on the particular polyphenolic materialused. If the polyphenolic material is an alkaline extract, for example,it can be largely in the form of already neutralized sodium salts of thepolyphenolic material, and only very small additional amounts of alkalimay be required. There is then added the formaldehyde compound, as forexample paraformaldehyde and this stock solution designated asDispersion A.

A particularly convenient modification of this procedure is provided byfirst preparing a solid powder of the polyphenolic material andparaformaldehyde together with minor amounts of fillers such as sodiumchloride and of various adjuvants such as preservatives, anti-dustingagents, antifoam agents and the like. This powder is then shipped to thegrouting site and used to prepare Dispersion A.

A second aqueous dispersion designated as Dispersion 8 is prepared withsufficient alkali to give substantially the same pH as in Dispersion Aand with the amount of gelling agent to give the required concentration. Just prior to the grouting operation and/or during injection, thetwo dispersions A and B are fed through metered pumps and mixedthoroughly. The volume ratio of the two solutions can be varied to suitthe application conditions which include density and porosity of soil,ambient temperature, mix-water temperature, and

the gel strength and grout strength desired.

An alternative procedure is to place the formaldehyde in the same stocksolution as the gelling agent.

It is, of course, possible to add all three principal components inseparate streams, but this has no particular advantage.

in order to gain maximum utility of the grouting operation it isextremely important to have accurate and close control of the length oftime between the mixture of dispersions A and B and the injection of themixture into the soil as well as of the time it takes to gel thecomposition. This control is made possible by controlling the relativeamount of gelling agent used. The dependence of gel-time upon theconcentration of the principal ingredients (polyphenolic, formaldehydeand gelling agent respectively) and in particular on the ratio ofgelling agent relative to polyphenolic as well as on temperature and pHare illustrated in the examples given further below. The presentinventors have found that the gel time can be varied at will from aboutone second to several hours by varying the type and amount of thegelling agent of this invention. Experiments have also shown that theinclusion of the gelling agent not only results in increased rate ofgelation but also effects an increased resistance of the groutedstructure to compressive forces. This increase in resistance to pressuregoes through a maximum as the proportion of gelling agent is increased.

The invention will be further described in connection with the followingexamples which are set forth for the purpose of illustration only. Inthese examples and elsewhere herein proportions are in parts by weightunless specifically stated to the contrary.

EXAMPLE 1 A powdered mixture was made containing 75 parts by weight ofmimosa extract, 13 parts of paraformaldehyde parts of sodium chloridetiller, 2 parts of dibutyl phthalate and 0.2 parts of carnea oil.

Twenty grams of this grouting powder was added to a solution of 3 gramssodium hydroxide in 67 grams of water. This solution is identified asSolution A.

To a solution of one gram sodium hydroxide in 96.5 grams of water therewas added 2.5 grams of vanadium pentoxide. Within about ten minutes aclear solution resulted. This solution is identified as Solution B.

The 90 grams of Solution A was added to the receptacle of a TecamGelation Meter, and 10 grams of Solution B was added thereto withthorough mixing. Thus, the weight ratio of the complexing elementvanadium to mimosa solids was 0.93 percent. The temperature of thesolutions before mixing was 2C. After mixing, the temperature reached6.5C. The pH was 1 1.8. The "gel time needed to develop resistance tothe fall of the plunger in the Tecam instrument was found to be 17.0minutes as compared to the 500 minutes required at this temperature whenSolution B is replaced by 10 grams of 1 percent aqueous sodium hydroxideand the gelling agent of the instant invention is absent.

EXAMPLE 2 The experiment of Example 1 was repeated excepting that theinitial temperature of the solutions before mixing was C. and thetemperature of the mixture reached 28C. The gel time was so short thatit was dif ficult to measure precisely, being of the order of 0.1

minutes, as compared to the 80-100 minutes required at 28C. without thehelp ofgelling agent.

EXAMPLE 3 The procedure of Example 2 was followed except that the 2.5grams of vanadium pentoxide in Solution B were replaced by 7.5 grams ofan aqueous sodium metasilicate solution. The mixture thus contained 0.67percent of elemental silicon based on the mimosa extract. Temperature ofthe solutions before mixing was 20C. the mixture reached 27C. and thegel time was 0.5 minutes.

EXAMPLES 4 8 The procedure of Example 2 was followed with the exceptionthat the gelling agent used in successive experiments was respectively(Ex. 4) potassium permanganate, (Ex. 5) manganous sulfate, (Ex. 6)sodium molybdate, (Ex. 7) zirconium tetrachloride and (Ex. 8) titaniumtetrachloride. in each case the pH of the mixture was in the rangebetween 9 and l l. The accompanying table summarized the respective (a)weight ratios of the complexing elements (W in gelling agents based ontannin (mimosa) extract solids (W (b) the pertinent temperatures and (c)the gel times. in all cases the gel time was shorter than the period of2 hours or more obtained in the absence of any gelling agent of thisinvention. The range of gel times illustrates the utility of the instantinvention in controlling gel time.

TABLE] r Weight ratio Temperature C. gel time Ex. W /W initial Mixed(mins) EXAMPLES 9-11 Three experiments using vanadium pentoxide asgelling agent are summarized in Table II. Solutions were preparedaccording to the procedures of Example 1 except that the amount ofvanadium pentoxide was varied so as to make the weight ratio of vanadiumelement to tannin solids equal to the values given in column (a) and thepH of the mixture, as recorded in column (b), was obtained bycorresponding adjustments in the alkali content. Gel times, given incolumn (c) were measured as before and comparative gel strengths after 2days, given in column (d), were evalu- EXAMPLE 2i A solution wasprepared from parts of spray dried mimosa extract, l.5 parts sodiumhydroxide, 83.5 parts water and 7.5 parts of a 36 percent aqueousformaldehyde solution. Aliquots of this solution C were mixed withdifferent amounts of percent aqueous solution of sodium silicate in theproportions given in the first column of Table VII and the correspondinggel times obtained at room temperature are recorded in the last columnof the same table.

TABLE VI EXAMPLE This example illustrates application of the presentinvention at 5C. 'Ihree forms of grout solution A were made as inexamples l5-20 by using respectively 15. 20 and 25 grams of the groutingpowder of Example 1. Two sets of such solutions and stock supplies ofvanadium pentoxide and sodium silicate solution were brought to 5C. Atthis temperature. amounts of the gelling agents were added to therespective grout solutions so as to make the weight ratio of complexingelement to mimosa tannin equal to the values of W /W, given in TableVIII. The corresponding gel times observed are recorded also in TableVIII.

TABLE VIII Vanadate and Silicate as Gelling Agents at 5C.

Gel Times With Different Levels of Sodium Silicate 20 Cone. of '5 GelTime (min) at 5C. Parts 20% NqSitl, w,,/w Gel Time Tlflmn Per l00 pansof '1: (mins.) n/ r mimosa l i C (m) Vanadate Silicate 1 25 n 3 4 2s 025 s s 0 3.27 0.67 6 1.96 .15 I50 2.40 .25 4.5 2 .654 [.20 18.7 0.8445.0 4.5

EXAMPLE 26 EXAMPLES 22-24 Three sets of experiments using sodiummolybdate as gelling agent at 25C were carried out with three differentlevels of the grouting composition, using respectively 15, 20 and 25grams of the grouting powder of Example 1 in formulating Solution A andusing amounts of sodium molybdate in Solution B such as to attain thevalues of W IW recorded in Table VII. The results as to gel time and gelstrength are also recorded in Table VII.

TABLE VII Molybdate as Gelling Agent at 25C. at Different Levels ofConcentration (m) of Tannin Solids A series of grouting solutions wasformulated with 15.0 percent mimosa tannin extract solids, 3.00 percentsodium hydroxide, 2.60 percent paraformaldehyde, 0.40 percent dibutylphthalate and sufiicient sodium silicate to make the ratio of siliconelement to tannin solids equal to the IN /W values respectively given inTable IX.

Each of these solutions was rapidly mixed with 50-60 mesh foundry sandin the weight proportions 3 parts sand to 1 part grouting solution. Thetreated sand was immediately placed in a 2-inch cubic mold and stored inmoisture saturated atmosphere (100% RH). After the storage periodsstated in the table, the grouted blocks were tested for their resistanceto pressure in a hydraulic press. The pressure reached when the blockcrumbled was taken to be the compressive strength of the groutedstructure. The results summarized in Table IX show that the inclusion ofthe gelling agent of this invention effects a substantial increase inthe compressive strength.

TABLE IX Effect of Na,Si0 Additions on Compressive Strength of SandGrouted with Tannin and Formaldehyde VI /W, Compressive Strength (psi)at at at 24 hrs 72 hrs I68 hrs 0.00 92 l00 0.09 95 90 I38 0.l7 I02 I53027 85 I02 I49 EXAMPLE 27 This example illustrates how variations in theproportion of the gelling agent of this invention can be used to controlthe degree of resistance to pressure. Grouting solutions were formulatedwith the proportions of tannin, paraformaldehyde, sodium hydroxide anddibutyl phthalate as used in Example 26 and were mixed at 25C. with thedifferent amounts of silicate or vanadate gelling agents correspondingto the information in Table X. Each mixture was allowed to set to aheight of about 4 inches in a metal tube 8 inches in height and 1.5inches in diameter and having in its base several slits of dimensionsapproximately 1 X A; inch and open at the top. The tubes containing gelwere filled to the top with water at 25C. and allowed to stand for aperiod of 24 hours. The tubes were then removed from the water and airpressure applied at the top of the tube. The pressure was increasedgradually until the gel broke down and was extruded through the slits.The results summarized in Table X clearly indicate that the presence ofthe gelling agent of this invention in the amounts used substantiallyincreased the pressure required to extrude the gel.

TABLE X Resistance of Grouting Gels to Pressure at 25C A glass tube fourfeet long and four inches in diameter was half filled with crushedgravel of size to it inches. Water was poured through the stones atapproximately half a gallon per minute, maintaining a steady state witha l-foot head of water above the stones.

An alkaline grouting solution was prepared in the proportions ofSolution A in Example l and placed in a storage vessel situated abovethe column. An alkaline solution of vanadium pentoxide was made similarto Solution B of Example 1 except that 5 parts of V were used per 100 ofsolution; this solution was placed in a second storage vessel. Therespective solutions were supplied under 5 psi pressure to a mixingchamber in the ratio of one part vanadate solution to three partsgrouting solution.

Immediately after mixing, the mixture was injected into the stone columnat about six inches below the surface of the stones. The positivepressure applied to the grouting solution displaced the flowing waterand permitted a gel to form rapidly around the injection point. Thegrouting solution spread from this point of injection into thesurrounding space and a plug of grouted stones built up quickly. Theflow of water was slowed down immediately and was reduced to one tenthof its original rate within five minutes. Further addition of groutsolution resulted in complete water cut-off. The gelled structuresupported a one-foot head of water for several days. This was in strongcontrast to the performance of a corresponding grouting solution notcontaining the gelling agent of this invention but otherwise having thesame composition; with such a solution it was impossible to form a gel,the solution being diluted by the flowing water before any gelling tookplace. Consequently no diminution in the flow of water was obtained.

It will be understood that it is intended to cover all changes andmodifications of the Examples of the invention herein chosen for thepurpose of illustration which do not constitute departures from thespirit and scope of the invention.

What we claim is:

l. A method for stabilizing soil which comprises A contacting the soilwith an aqueous alkaline gelforming composition containing a. apolyphenolic vegetable material selected from the group consisting oftannin extracts, catechins and alkaline extracts of coniferous treebarks, said polyphenolic material being soluble in alkaline solution,able to gel rapidly and having a formaldehyde combining capacity of atleast 5.0,

b. a fonnaldehyde compound selected from the group consisting offormaldehyde, paraformaldehyde and water-soluble phenolformaldehyderesoles and a gelling agent soluble or colloidally dispersible in saidcomposition and containing a complexing element selected from the groupconsisting of silicon, vanadium, molybdenum, manganese, titanium,copper, zinc and zirconium, said complexing element being proportionedto control the gelling rate; wherein when silicon is selected as thecomplexing element, the gelling agent is selected from the groupconsisting of the silicates of sodium, potassium, lithium and ammonium;and

B. allowing the treated soil to form a substantially compact mass.

2. The method of claim 1 wherein the concentration of the polyphenolicmaterial in the aqueous composition is between about 2 and 45 percentwherein the formaldehyde compound is either formaldehyde orparaformaldehyde in amount between about 5 and 30 percent based on thedry weight of polyphenolic material or between about 10 and percent of aresole, and wherein the complexing element is present in an amountcorresponding to between about 0.01 and 10 percent based on the weightof dry polyphenolic material.

3. The method of claim 1 wherein the gelling agent is sodium silicate.

4. The method of claim 1 wherein the polyphenolic material is selectedfrom the group consisting of the vegetable tannin extracts of mimosa,quebracho, mangrove and wattle.

5. The method of claim 1 wherein the polyphenolic material is selectedfrom the group consisting of the catechin extracts of acacia catechu,acacia suma and mahogany wood.

6. The method of claim 1 wherein the polyphenolic material is selectedfrom the group consisting of the alkaline extracts of the barks ofWestern Hemlock, Douglas Fir, Sitka Spruce and Southern Yellow Pine.

7. The method of claim 1 wherein the polyphenolic material is theextract of mimosa.

8. The method of claim 1 wherein said gelling agent is selected from thegroup consisting of vanadium pentoxide, potassium vanadate, sodiumvanadate, lithium vanadate and ammonium vanadate.

9. The improved soil-grouting process which comprises injecting intosoil to be stabilized and/or strengthened, an aqueous alkalinegel-forming composition consisting essentially of a mixture ofpolyphenolic material selected from the group consisting of thevegetable tannin extracts of mimosa, quebracho, mangrove and wattle,catechin tannins and the alkaline extracts of coniferous barks,dispersed in sufiicient water to form a 2 to 45 percent solution byweight, said polyphenolic material being substantially soluble inalkaline aqueous solution, being capable of rapid gelation and having afonnaldehyde combining capacity of at least 5.0; from 5 to 30 percent offormaldehyde based on weight of dry polyphenolic material; and a gellingcompound soluble or colloidally dispersible in said aqueous compositionwhich provides in the composition a complexing element selected from thegroup consisting of silicon, vanadium, molybdenum, manganese titanium,copper, zinc or zirconium, the amount of said complexing element in saidcomposition being within the range of from about 0.01 to l0 percentbased on the dry weight of the solid polyphenolic material, saidcomposition being thoroughly mixed before injecting it into the soil,said complexing element being proportioned to effect the gelling rate.

10. The process for preparing a gel in association with a mass of solidparticles which process comprises: intermixing a vegetable tanninextracted from mimosa with sufficient water to form a 7-23 percentsolution by weight; intcrmixing with said solution from to 25 percent ofparaformaldehyde based on the dry weight of mimosa extract and a gellingcompound soluble or colloidally dispersible in said solution in amountsufficient to provide from 0.1 to 6.5 percent based on dry weight ofmimosa extract of a complexing element of the group consisting ofsilicon and vanadium, said element accelerating the gel-forming reactionof the composition, said element being selected in such an amount as tocontrol the gelling rate at the temperature of said solid particles; andpromptly before any appreciable reaction takes place, injecting theintermixed components into the mass of solid particles to form a stablegel structure.

11. A method for stabilizing soil which comprises A. contacting the soilwith an aqueous alkaline gelforming composition containing a. apolyphenolic vegetable material selected from the group consisting oftannin extracts, catechins and alkaline extracts of coniferous treebarks, said polyphenolic material being soluble in alkaline solution,able to gel rapidly and having a formaldehyde combining capacity of atleast 5.0, b. a formaldehyde compound selected from the group consistingof formaldehyde, paraformaldehyde and water-soluble phenolfonnaldehyderesol and c. vanadium pentoxide; and

(B) allowing the treated soil to form a substantially compact mass.

12. A method for stabilizing soil which comprises A. contacting the soilwith an aqueous alkaline gelforming composition containing dissolved ordispersed therein a. a polyphenolic vegetable material selected from thegroup consisting of tannin extracts, catechins and alkaline extracts ofconiferous tree barks, said polyphenolic material being soluble inalkaline solution, able to gel rapidly and having a formaldehydecombining capacity of at least 5.0,

b. a formaldehyde compound selected from the group consisting offormaldehyde, paraformaldehyde and water-soluble phenolformaldehyderesoles and c. a water-soluble gelling agent selected from the groupconsisting of sodium and potassium silicates; and

B allowing the treated soil to form a substantially compact mass.

1|! i 1" lK 1|:

2. ThE method of claim 1 wherein the concentration of the polyphenolicmaterial in the aqueous composition is between about 2 and 45 percentwherein the formaldehyde compound is either formaldehyde orparaformaldehyde in amount between about 5 and 30 percent based on thedry weight of polyphenolic material or between about 10 and 90 percentof a resole, and wherein the complexing element is present in an amountcorresponding to between about 0.01 and 10 percent based on the weightof dry polyphenolic material.
 3. The method of claim 1 wherein thegelling agent is sodium silicate.
 4. The method of claim 1 wherein thepolyphenolic material is selected from the group consisting of thevegetable tannin extracts of mimosa, quebracho, mangrove and wattle. 5.The method of claim 1 wherein the polyphenolic material is selected fromthe group consisting of the catechin extracts of acacia catechu, acaciasuma and mahogany wood.
 6. The method of claim 1 wherein thepolyphenolic material is selected from the group consisting of thealkaline extracts of the barks of Western Hemlock, Douglas Fir, SitkaSpruce and Southern Yellow Pine.
 7. The method of claim 1 wherein thepolyphenolic material is the extract of mimosa.
 8. The method of claim 1wherein said gelling agent is selected from the group consisting ofvanadium pentoxide, potassium vanadate, sodium vanadate, lithiumvanadate and ammonium vanadate.
 9. The improved soil-grouting processwhich comprises injecting into soil to be stabilized and/orstrengthened, an aqueous alkaline gel-forming composition consistingessentially of a mixture of polyphenolic material selected from thegroup consisting of the vegetable tannin extracts of mimosa, quebracho,mangrove and wattle, catechin tannins and the alkaline extracts ofconiferous barks, dispersed in sufficient water to form a 2 to 45percent solution by weight, said polyphenolic material beingsubstantially soluble in alkaline aqueous solution, being capable ofrapid gelation and having a formaldehyde combining capacity of at least5.0; from 5 to 30 percent of formaldehyde based on weight of drypolyphenolic material; and a gelling compound soluble or colloidallydispersible in said aqueous composition which provides in thecomposition a complexing element selected from the group consisting ofsilicon, vanadium, molybdenum, manganese, titanium, copper, zinc orzirconium, the amount of said complexing element in said compositionbeing within the range of from about 0.01 to 10 percent based on the dryweight of the solid polyphenolic material, said composition beingthoroughly mixed before injecting it into the soil, said complexingelement being proportioned to effect the gelling rate.
 10. The processfor preparing a gel in association with a mass of solid particles whichprocess comprises: intermixing a vegetable tannin extracted from mimosawith sufficient water to form a 7-23 percent solution by weight;intermixing with said solution from 15 to 25 percent of paraformaldehydebased on the dry weight of mimosa extract and a gelling compound solubleor colloidally dispersible in said solution in amount sufficient toprovide from 0.1 percent to 6.5 percent based on dry weight of mimosaextract of a complexing element of the group consisting of silicon andvanadium, said element accelerating the gel-forming reaction of thecomposition, said element being selected in such an amount as to controlthe gelling rate at the temperature of said solid particles; andpromptly before any appreciable reaction takes place, injecting theintermixed components into the mass of solid particles to form a stablegel structure.
 11. A method for stabilizing soil which comprises A.contacting the soil with an aqueous alkaline gel-forming compositioncontaining a. a polyphenolic vegetable material selected from the groupconsisting of tanNin extracts, catechins and alkaline extracts ofconiferous tree barks, said polyphenolic material being soluble inalkaline solution, able to gel rapidly and having a formaldehydecombining capacity of at least 5.0, b. a formaldehyde compound selectedfrom the group consisting of formaldehyde, paraformaldehyde andwater-soluble phenolformaldehyde resoles and c. vanadium pentoxide; andB. allowing the treated soil to form a substantially compact mass.
 12. Amethod for stabilizing soil which comprises A. contacting the soil withan aqueous alkaline gel-forming composition containing dissolved ordispersed therein a. a polyphenolic vegetable material selected from thegroup consisting of tannin extracts, catechins and alkaline extracts ofconiferous tree barks, said polyphenolic material being soluble inalkaline solution, able to gel rapidly and having a formaldehydecombining capacity of at least 5.0, b. a formaldehyde compound selectedfrom the group consisting of formaldehyde, paraformaldehyde andwater-soluble phenolformaldehyde resoles and c. a water-soluble gellingagent selected from the group consisting of sodium and potassiumsilicates; and B. allowing the treated soil to form a substantiallycompact mass.